MOSCOW — Scotland Yard called the radiation poisoning of former Russian intelligence agent Alexander Litvinenko a murder Wednesday, as Russian and British investigators questioned a witness in the case in Moscow.

Two weeks after Litvinenko’s death, the trail of trace amounts of the radioactive substance polonium-210 continued to expand Wednesday, as authorities said they discovered tiny amounts at a London soccer stadium and the British Embassy in Moscow.

Litvinenko’s family, meanwhile, prepared for his funeral, as friends described his deathbed conversion to Islam.

The 43-year-old Litvinenko, a critic of Russian President Vladimir Putin, died Nov. 23 in London, where he lived in self-imposed exile.

After his death, a friend read a statement in which Litvinenko called Putin “the person responsible” for his death. The Kremlin denied the allegation.

The investigation began even before the radioactive poison killed Litvinenko, but until Wednesday police had not formally declared the case a homicide.

‘An allegation of murder’
“Detectives ... have reached the stage where it is felt appropriate to treat it as an allegation of murder,” London’s Metropolitan Police said in a statement. “It is important to stress that we have reached no conclusions as to the means employed, the motive or the identity of those who might be responsible for Mr. Litvinenko’s death.”

Interfax news agency reported that British and Russian investigators on Tuesday and Wednesday interrogated Dmitry Kovtun, one of at least two Russian businessmen who met Litvinenko in London’s Millennium Hotel on Nov. 1, hours before he fell ill.

Kovtun and an associate, Andrei Lugovoi, have told the Russian media they went to London as part of a group of Moscow soccer fans, and met briefly with their exiled countryman to discuss business matters. Later, they attended a match between CSKA Moscow and Arsenal at the Emirates Stadium in north London.

Both men have told reporters in Moscow that someone is trying to frame them in Litvinenko’s death.

Boris Berezovsky, a flamboyant Russian tycoon and political foe of Putin, routinely entertains friends and associates in a private box at the stadium. Litvinenko joined Berezovsky’s emigre circle after fleeing Russia in 2000.

Lugovoi is thought to have asked Berezovsky for tickets, but the tycoon’s box was full and Lugovoi’s party of eight received tickets to seats elsewhere in the stadium.

Stadium is latest polonium site
Authorities on Wednesday added the stadium to a list of more than a dozen sites in London where traces of polonium-210 have been found.

Katherine Lewis, spokeswoman for Britain’s Health Protection Agency, said substance was found in two sites in the stadium, but did not specify where. She said radiation levels were “barely detectable” and posed no public health risk.

British officials also said Wednesday that a room in the British Embassy in Moscow showed traces of a radioactive substance, although there was no threat to public health.

Kovtun and Lugovoi visited the embassy last month to discuss the Litvinenko case with embassy officials. Lugovoi recently told the ITAR-Tass news agency that he is undergoing tests for radiation contamination and that the results would be available in a few days.

ITAR-Tass said Lugovoi expected to be interviewed by investigators Thursday. He said he is ready to answer all questions.

In London, traces of polonium-210 were also found at a private security firm, a sushi bar and in Berezovsky’s offices.

Minute amounts of the radioactive substance were also discovered on British Airways planes that flew from Moscow to London on Oct. 31 and from London to Moscow on Nov. 3, the day Lugovoi says he returned to Russia.

Witnesses interviewed
Interfax reported Tuesday that Lugovoi had not yet been questioned, quoting his lawyer, Andrei Romashov. The Russian Prosecutor-General’s Office confirmed in a brief statement that it had started questioning potential witnesses in the Litvinenko case.

ABC News quoted an unidentified British official as saying Lugovoi, a security expert whose business interests include a share of a beverage and wine plant in Russia, was the “prime suspect” in the investigation.

However, a British official told The Associated Press on Wednesday that “Lugovoi is one of many people investigators are looking to question, but I wouldn’t call him a suspect at this point.”

The official, who requested anonymity because he is not authorized to speak to the media, added: “We’re also looking at the possibility there were criminal gangs involved.”

A former KGB officer, Lugovoi told Ekho Moskvy radio that he had known Litvinenko for a decade. Their acquaintance dated to Lugovoi’s tenure as chief of the security detail at ORT, the Russian television network that Berezovsky controlled before the tycoon fell out with Putin.

Berezovsky fled to London to avoid what he claims are politically motivated money-laundering charges. He was granted political asylum in 2003.

Lugovoi, meanwhile, served a brief jail term in 2002 for allegedly helping an executive of Aeroflot airlines — then partly controlled by Berezovsky — escape from pretrial detention.

Contact with LitvinenkoLugovoi has told the Russian media that Litvinenko contacted him about a year ago with business-related proposals. He said they had met intermittently in London since then.

Litvinenko was a counterintelligence officer with the Federal Security Service, or FSB, the main successor agency to the KGB, when he broke with the agency in 1998. At a press conference, he accused his bosses of ordering him to kill Berezovsky.

In 2004, Litvinenko wrote a book accusing the FSB of orchestrating the bombing of Russian apartment buildings in 1999, allegedly to stir up support for Russia’s second war against Chechen separatists.

After journalist Anna Politkovskaya, a critic of Putin and Russia’s war in Chechnya, was shot to death in Moscow in October, Litvinenko began an independent investigation.

Meanwhile, Lugovoi traveled to London three times in the month before Litvinenko’s death, and met with him four times, according to the Russian media.

Romashov, Lugovoi’s lawyer, denied Wednesday that his client was a suspect.

In London, Alexander Goldfarb, a friend of Litvinenko’s who helped him escape Russia, said he doubted Lugovoi was the killer.

“I frankly doubt that he was the hit man because hit men are usually people hiding in the dark,” Goldfarb told the AP. “I think it’s one of his associates, I think he was used unawares. ... Now his life is in danger because he knows a lot.”

Kovtun, the man reportedly questioned Tuesday and Wednesday, told Ekho Moskvy radio last month that Lugovoi had introduced him to Litvinenko in October in London, where Kovtun had business interests.

Long-time friends
Kovtun and Lugovoi have known each other since their days together at a military academy. Kovtun said he was helping Western companies enter the Russian market, and that Litvinenko had introduced him to officials with two British companies.

Kovtun said he, Lugovoi and Litvinenko had dinner in London’s Chinatown on Oct. 16 or 17. The only other time he saw Litvinenko, Kovtun said, was Nov. 1, before the soccer match.

Litvinenko’s father, Walter, told Radio Liberty his son had converted to Islam and wanted a Muslim burial. “He told me about his decision two days before he died. He said, ’Papa, I have to talk to you about something serious. I’ve become a Muslim.”’

An ally of Litvinenko said the ex-spy converted on his deathbed.

“He told me that he wanted to convert to Islam literally in his first days in the hospital,” said Chechen rebel envoy Akhmed Zakayev. “I did not pay a lot of attention to this,” Zakayev told Radio Liberty, “but he returned to the theme again and again.”